Fig. 1. Monoclonal antibodies distinguish two populations of muscle cells in Xenopus. Transverse cryosections of stage 35 (A-E), stage 48 trunk (F,G) and adult hindlimb muscle (H-J) stained with monoclonal antibodies to all skeletal muscle MyHC isoforms (A), MyHC of the myotomal superficial muscle fibre monolayer (B-D,F,I,J), MyHC of the deep muscle layers (D,F, green) and NADH-TR histochemistry of adjacent serial sections showing fibres with high mitochondrial enzyme content (E,G,H). (A-G) Two antibodies (BA-F8 and EB165) preferentially label the outermost muscle fibre layer (arrowheads, A-D,F). Note that the superficial layer develops oxidative metabolism (arrowheads E,G). (H-J) In adult muscle, oxidative fibres weakly express MyHC immunologically, similar to the superficial muscle layer in the larvae (asterisks), whereas glycolytic fibres show only background staining (dots). (K,L) Whole-mount immunohistochemistry reveals that a subset of all muscle fibres marked by the 12/101 muscle marker (K) express the EB165 epitope (L). Note the EB165 expression at the leading edge of the abdominal fibre layer (arrowhead) and its lack in more dorsal fibres (asterisk) at stage 48. A subset of head fibres express slow (EB165). NT neural tube; not, notochord; e, eye; i, intestine; j, jaw; s, somite.